Dumb Science Question du Jour

Earlier this evening, I took Charlie and Ruairi over to the playground of one of our local schools for a little knockabout hockey practice - injecting some much-needed life into the work/life balance.

On the way there, we all noticed the contrail of a jet, high in the clear sky, as the plane passed above the clear, bright moon. Walking East, we noticed how the line of the contrail seemed to be moving down the sky, appearing to cross in front of the moon and then steadily sink below it, while the jet continued to arc across the firmament.

Thinking we were witnessing some kind of parallax effect due to the fact that we were still moving as we gazed upwards, we stopped. The gap between the roughly straight line of the contrail and the moon, however, continued to widen - slowing down, but still moving further away from the "fixed" point at which we'd first observed it.

Was this phenomenon caused by high altitude wind, somehow pushing the entire contrail evenly across the sky? Or were we perhaps witnessing, as Charlie suggested, simple but pleasingly startling evidence of the Earth's rotation?

And while you're noodling that one, Ruairi (4) would like to know if it was really a plane we saw, or was it Buzz Lightyear...